1A1

The Tektronix Type 1A1 plug-in for the 500-series scopes has two channels and a −3 dB point of 50 MHz at 50 mV/Div, 28 MHz at 5 mV/Div, and 2 Hz to 15 MHz at 500 μV/Div when channels 1 and 2 are cascaded. It was designed by Ron Olson.

There were three distinct versions of 1A1.

• The first version, from 1964 to 1966, has a Nuvistor front-end, and rotary input switches that were concentric with the BNC jacks. The knobs to invert the input channels are concentric with the vertical position knobs.
• The second version, from 1966 to ??? has fluted round V/cm knobs, and lever switches. The channel inversion control is an organ-style pull-push knob. The nuvistors are mounted under a thermal cover on a sub-chassis with rubber stand-offs.
• The third model, from ??? until the end has four-sided V/cm knobs and a FET front-end.

Type 1A1 uses the "ALT SWEEP SLAVE PULSE" signal that is sent by scopes on pin 7 of the plug-in connector. In a Type 547 mainframe, this signal allows channel 1 to be displayed using the "A" timebase and channel 2 using the "B" timebase. This is useful, for example, to view the IF and AF of a radio receiver at the same time. Even after the front-end transitioned from Nuvistors to FETs, the output amplifier continued to use Nuvistors.

Type 1A1 has an External Trigger output for mainframes prior to the 547 that don't support plug-in triggering, and supplies the trigger system on pins 4/5 of the mainframe interface. It also has a ×10 amplified output from channel 1 that can be cascaded into the channel 2 input for 500 μV/Div sensitivity at reduced bandwidth (15 MHz).

Types 1A1 and 1A2 were introduced together in 1964, the former for high-end use, the latter as an upgrade/replacement for Type CA. Both remained available until the 500-series scope line was discontinued.

The 1A1 is not a perfect superset of the 1A2; it supplies external trigger from channel 1 only.

The 1A1 may have evolved from the Type J, which never went into production.

Key Specifications

Bandwidth	50 MHz @ 50 mV/Div and up (in fast mainframes), 28 MHz @ 5 mV/Div, 15 MHz with cascaded channels (~0.5 mV/Div)
Rise time	7 ns @ 50 mV/Div and up (in fast mainframes), 13 ns @ 5 mV/Div, 24 ns with cascaded channels (~0.5 mV/Div)
Deflection	5 mV/Div to 20 V/Div, 1−2−5
Max. input	600 V DC + peak AC
Input impedance	1 MΩ // 15 pF
Modes	Ch 1, Ch 2, ALT, CHOP, ADD

Links

• 1A1 @ amplifier.cd

Pictures

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  1A1 SN121

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  Early 1A1

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  Second 1A1 version

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  left: Nuvistor right: FET

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  left: Nuvistor right: FET

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  left: Nuvistor right: FET

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  Nuvistors under thermal cover, on shock-mounted sub-chassis

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  Nuvistor cover and tubes unplugged

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  Nuvistor cover and tubes, bottom

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  Early 1A1 front end

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  Late 1A1 Output Amp

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  Early 1A1 Left View

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  Latest version of 1A1

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  556 with second version 1A1 in left bay and first version 1A1 in right bay.

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  Black 1A1

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  Latest version 1A1. Photo courtesy of Dan Wilson (Hideaway Studio).

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  1A1 - First Version - Top

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  1A1 - First Version - Underside

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  1A1 - First Version - RHS

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  1A1 - First Version - LHS

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  Input FET board CH1

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  Input FET board CH2